1. Field of the Invention
The present invention relates to a semiconductor laser device and a manufacturing method thereof.
2. Background Art
FIG. 10 is a perspective view illustrating a conventional semiconductor laser bar 100. The semiconductor laser bar 100 shown in FIG. 10 is provided with a semiconductor laser bar body 101, a front facet coating film 102 and a back facet coating film 103. A scribed track 104 is formed on one side of the semiconductor laser bar 100 and a blade 105 is placed on the opposite side thereof. The scribed track 104 is often drawn on a substrate surface side of the semiconductor laser bar body 101. By adding a force through the blade 105 to divide the semiconductor laser bar 100, it is possible to form a semiconductor laser chip 101a or a semiconductor laser mini bar.
The aforementioned conventional semiconductor laser device 100 has a uniformly flat facet and a coating film is provided on this facet. Normally, a division is made by applying scribing to a semiconductor laser bar after the coating film is provided.
The division is performed by pressing the blade 105 against a crystal growing surface which is opposite to a substrate surface on which the scribed track 104 shown in FIG. 10 is drawn so as to bend the semiconductor laser bar 100. The back facet coating film 103 is generally thicker than the front facet coating film 102. This is because low reflectivity is adopted for the front facet and high reflectivity is adopted for the rear facet so that more light is emitted from the front facet. A material for the front facet coating film 102 and the rear facet coating film 103 is an oxide, which is different from a semiconductor material for a semiconductor laser element body in material physical properties such as rigidity, Young's modulus and Poisson ratio. For this reason, regarding a substrate surface, the semiconductor laser bar body 101 and the rear facet coating film 103 are not simultaneously split when a division is started, and one of the two is split first.
FIG. 11 is a diagram illustrating an element division step of the conventional semiconductor laser bar 100. FIG. 11 shows a case where the rear facet coating film 103 is split first, but there is also a case where the semiconductor laser bar body 101 is split first. However, since these parts are not simultaneously split in anyway, on the corners on the semiconductor substrate side on which the scribed track 104 is formed, adhesion between the rear facet coating film 103 and the semiconductor laser bar body 101 is always weak or the rear facet coating film 103 is peeled.
The divided semiconductor laser chip 101a or semiconductor laser mini bar or the like are generally die-bonded to a submount 106 using solder. In this case, after being heated to a temperature equal to or higher than a melting point of the solder, the semiconductor laser chip 101a or semiconductor laser mini bar are bonded to the submount 106. Since the material of the coating film is different from the material of the semiconductor laser in material physical properties such as thermal expansion coefficient, distortion occurs in the coating film during heating and if the distortion exceeds a certain value, the coating film is easily peeled away from the facet of the semiconductor laser chip. The distortion value increases as the thickness of the coating film increases.
FIG. 12 is a diagram illustrating a coating film of a conventional semiconductor laser chip which has been peeled after die bonding, showing a semiconductor laser device obtained by bonding the semiconductor laser chip 101a and the submount 106 after being heated at 340° C. for 60 seconds. FIG. 12 illustrates the semiconductor laser chip 101a, the submount 106, a crystal growing surface side portion 107a of the semiconductor laser chip 101a and a substrate surface side portion 107b of the semiconductor laser chip 101a. FIG. 12 illustrates how the rear facet coating film is peeled on the corners of the substrate surface side portion 107b of the semiconductor laser chip 101a. 
FIG. 13 is a diagram illustrating the coating film of the conventional semiconductor laser mini bar 101b which has been peeled. FIG. 13 shows the semiconductor laser mini bar 101b which has been heated at 390° C. for 30 seconds. FIG. 13 shows an example where the semiconductor laser mini bar 101b is simply heated at 390° C. for 30 seconds without being bonded to the submount 106. FIG. 13 shows how the rear facet coating film 108b on the corner on the substrate surface side is peeled as with the semiconductor laser chip 101a. 
A similar phenomenon can also occur with the front facet coating film, but since the phenomenon is more prominent in the rear facet coating film which is thicker, the rear facet coating film has been described in the present Description of the Related Art by way of example.
Other prior art in relating to a semiconductor laser device includes Japanese Laid-Open Patent Publication No. 2012-64886. Although Japanese Patent Laid-Open No. 2012-64886 describes a semiconductor laser device having a groove, there is no description relating to the aforementioned peeling of the coating film.
As described above, when the conventional semiconductor laser bar 100 is divided after applying scribing thereto, an insufficient bonded region appears between the coating film and the semiconductor laser element body on corners of the chip of the semiconductor laser device. If the semiconductor laser device which has become a chip after the division is bonded to the submount 106 or the like using solder, there is a problem that the coating film is peeled caused by this insufficient bonded region.